This invention relates to code responsive logic circuits for operation of lock mechanisms.
There are many applications which require complex and changeable lock systems. For example, in large hotels it is the current practice to provide each room with a standard mechanical tumbler lock. A guest is provided with a key which matches only the lock to the room he is assigned. As keys are lost or taken inadvertently, new keys must be made, which is a time consuming and costly operation. Further, theft poses a very substantial problem. It is often necessary to change or re-key door locks when it is suspected that keys may have fallen into unauthorized hands.
A further complication in such a system is imposed by the usual necessity of a number of levels of master keys. In a hotel, for example, a maid must be provided with a master key which unlocks rooms she services; for security reasons, however, it is generally desirable to provide her with a master key which opens only the rooms to which she is assigned and no others. A supervisor of maids may be given a higher level master key which opens the rooms assigned to all persons under her supervision. Still higher level master keys may be given to hotel personnel, each for opening all doors in a large section of the hotel in case of fire. Finally, there may be a highest level master key which will open all doors.
It may be seen, then, that the requirement of a number of levels of master keys and the recurrent need to change individual door locks or groups of door locks to control theft presents a very substantial problem. Skilled locksmiths must be employed on a virtually constant basis. Because of the cost and time involved in changing locks, however, there is a resulting reluctance to make such changes. As a consequence, security against unauthorized entries and thefts is often lessened.
The problems encountered in the example given are found in any present security system in which standard mechanical locks are used. The application of the system and the types of master levels involved may vary, but the problems remain.
A number of electrically controlled systems have been proposed to meet some of the problems mentioned above. The simplest type uses a decoding device mounted adjacent to each door lock which may be pre-set. A binary combination number is set into each device by, for example, simple switches. A user operates a push-button key switch or inserts a card-type key on which a number is binarily encoded. If a comparison between the entered key number and the previously stored combination number finds the numbers equal, the door is unlocked.
Such a system is an improvement over the mechanical lock systems described above in that each door lock may be more easily changed or re-keyed. However, to change a combination, each door lock must be opened by security personnel as with a mechanical system. Further, such systems have no provision for various levels of master keys or combinations. Also, since most such systems protect the re-keying switches with a mechanical lock, many of the above problems remain.
Another type of electrically controlled system utilizes similar key and decoding hardware, but transmits entered key combinations to a central location where they may be checked by a computer. If the entered combination is a proper one, the lock is opened under computer control.
A further type similar to the centrally controlled system described above controls a change in a door combination when a new key is issued. In this system, the new combination is transmitted to a door lock memory device as the key is produced.
The disadvantage to the centrally controlled type of system is that the control device must be connected by cables to each lock. While this is reasonable in a small system, its use in a large building complex or in any application requiring a greater number of controlled locks is very expensive. Also, in both large and small installations, connecting cables are vulnerable to tampering. Moreover, such a system cannot be used in any application where direct connection with a controlled lock is impossible, as in a fleet of vehicles. Further, as the numbers of controlled locks grow, larger central computers and, in some instances, multiplexing systems, are required which also greatly increases system costs.